1. Field of the Invention
This invention relates to desolderers and heater assemblies for use therewith.
2. Discussion of the Prior Art
In FIG. 1, there is illustrated a desolderer which corresponds to that shown in FIG. 6 of U.S. Pat. No. 3,392,897 granted to W. J. Siegel and assigned to the assignee of the present application, the foregoing patent being incorporated herein by reference. Other prior art references of interest related to U.S. Pat. No. 3,392,897 are U.S. Pat. Nos. 3,422,247; 3,469,759 and 4,023,724.
Referring to FIG. 1, the desolderer 10 may comprise a removable tubular tip 12 which extends forward from a heater assembly 14. Rearward of heater assembly 14 is thermal baffle assembly 16, then handle assembly 17 and finally a vacuum fitting assembly 19.
Referring to heater assembly 14, a metallic tube 50 may have a resistance wire heating element 49 wound thereabout and an insulating ceramic 54 around the resistance wire where elements 49 and 54 together comprise heating element 52. Tube 50 may be formed by machining down one end of a bi-metallic tubular blank, having an outside tube of copper and an inner thinner tube of steel, to the relatively thin steel tube at rear end portion 51. At the untouched central portion 53 of the copper-steel bi-metallic tube, resistance wire 52 and ceramic insulator 54 may be placed. A terminal shoulder or flange 60 on which a sleeve 62 seats may be provided on a thick forward end portion 56 of tube 50.
A plurality of elongated circumferential slits 64 may be cut into sleeve 62 near the rearward terminus thereof to provide a thermal barrier between the front and rear ends of sleeve 62. In a similar manner the thin character of the wall at rear portion 51 of tube 50 acts to diminish conduction of heat rearward from resistance heater wire 52.
Axially rearward of sleeve 62 is thermal barrier assembly 16 formed by a pair of axially spaced apart circular plates 18 (metal) and 20 (non-metallic). Plates 18, 20 may each have a relatively large central aperture therein. The plates 18 and 20 may be maintained in their spaced apart relation by a plurality of screws 22 (or bolts) and spacer elements 24 symmetrically disposed near the periphery of plates 18, 20. At its rearward terminus sleeve 62 is attached (e.g. press fit, swaged, etc.) to plate 18 at the bounding edge of its central aperture. The essentially open air space provided between plates 18, 20 acts as thermal insulation between sleeve 62 and handle assembly 17 of solder extractor 10. Moreover the same air space acts to cool the exposed rear portion 51 of central tube 50 which extends through the central apertures of plates 18, 20.
A hollow hub 28, desirably of non-metallic construction (e.g. wood, bakelite), may be mounted on the back face of plate 20. The rearmost extent of tube 50 passes through the central aperture in plate 20 to a termination inside hub 28 at a forward seal 30, which may be of silicone rubber. Seal 30 is disposed between the bounding edges of the central aperture on plate 20 and hub 28 being maintained there by a washer member 31 which bears against the flanged rim of seal 30 and the body of hub 28 at recesses 33 therein.
Rearwardly of hub 28 from a circular seat thereon extends tubular handle grip 32 which may be formed of glass or of a transparent plastic. Handle grip 32 and hub 28 are the held parts of solder extractor 10. The power supply cord 28 may end at a junction box 34 mounted at the end of grip 32. From junction box 34 electrical leads 36 pass inside handle grip 32 then internally of hub 28, through an aperture in plate 20 and inside of sleeve 62 to the resistance wire heating element 52. The ground wire may be grounded to rear portion 51 of tube 50.
Central tube 50 extends rearwardly into hub 28 to forward seal 30. Seated on forward seal 30 is a solder collection chamber 72. This solder catcher tube 72 may comprise an elongated open cylinder which is sealed at its forward end by seating on forward seal 30 and at its rearward end by seating on the hollow (rubber) rear seal 80. A passage for flow of molten solder is provided by tip 12, tube 50 and chamber 72. Application of vacuum to vacuum fitting assembly 19 at the rear of chamber 72 transmits suction to the forward end of tip 12.
The vacuum fitting assembly 19 may include rear seal 80. Extending therethrough may be a baffle tube 82 whose front end is shaped into a flat imperforate base 90 and a reduced neck 92 having a radial hole 94. Rearward of seal 80 may be a spring biased bayonet lock formed by a spring 100, spring plate 102, a grooved stop or retainer 104 and lock member 105. The vacuum fitting assembly serves to retain chamber 72 inside handle grip 32 but readily removable therefrom.
In operation, desolderer 10 is applied in a well known manner to a terminal or the like which is to be desoldered. Although desolderer 10 is useful in many applications, it is desirable in many instances to work in very close quarters where the operator must be able to exercise fine control over the desoldering operation. The operator is aided in doing this, the shorter the tip-to-grip dimension is. This dimension is indicated in FIG. 1.
Accordingly, it is an important object of this invention to provide an improved desolderer having a short tip-to-grip dimension to thereby permit the operator to exercise more control over the desoldering operation.
As will be brought out in more detail hereinafter, a shortened tip-to-grip dimension is compatible with the employment of a smaller heater 52 whereby less wattage is needed to produce the same tip temperature as that produced by desolderer 10 of FIG. 1. Further, not only does the smaller heater make the desolderer more efficient but it also has less tendency to raise the temperature of handle 32. Since the handle temperature typically should not rise above about 120.degree. F. to ensure operator comfort, this, of course, is another important advantage of being able to employ a smaller heater.
Accordingly, it is another important object of this invention to provide an improved desolderer having a small heater whereby the desolderer operates more efficiently than conventional desolderers while at the same time there is less tendency for the handle of the desolderer to rise to an uncomfortable temperature for the operator.
It has typically been necessary to employ a relatively high wattage heater 52 in desolderer 10 of FIG. 1 so that the heat produced by heater 52 raises not only the temperature of tip 12 to a point where solder can be melted but also raises the temperature of the rear end 51 of tube 50 to a point where the molten solder will remain molten as it traverses from tip 12 to rear end portion 51 under the influence of the vacuum applied through assembly 19. Otherwise, the molten solder will tend to solidify before it reaches rear end portion 51 and thus clog or otherwise impede the passageway through tube 50.
It is thus a further object of this invention to provide an improved desolderer wherein a small heater may be employed and yet the tip and rear end of the solder transfer tube thereof are both maintained at at least the solder melting temperature.
Not only is it desirable to maintain both the tip and the rear end of the solder transfer tube at the solder melting temperature, but it is also desirable the tip be maintained at a temperature higher than that of the rear end of the transfer tube. Otherwise, the intermediate portion of the desolderer tends to draw more heat from the heater 52 than does tip 12 whereby the heater efficiency is diminished and the intermediate portion of the desolderer tends to overheat.
It is thus a further object of this invention to provide an improved desolderer wherein the tip is maintained at a higher temperature than the rear end of the solder transfer tube.
It is further desirable that the rear end of the solder transfer tube be raised to the solder melting temperature shortly after the temperature at tip 12 is raised to this temperature. When the FIG. 1 desolderer is first energized, tip 12 may reach the solder melting temperature in three minutes, for example, while rear end portion 51 may sometimes require 15 minutes, for example, to reach this temperature. Thus, if the operator uses the desolderer six minutes after it has been energized, he will initially be able to desolder a terminal connection; however, due to the fact that rear portion 51 has not reached the solder melting temperature, the molten solder formed at tip 12 may re-solidify in tube 50 before it reaches rear portion 51. Such solidification of the solder in tube 50 may cause blockage and is, of course, contrary to the desired object of maintaining the solder in its molten state until it reaches tube 72 where it may be collected.
Thus, it is a further object of this invention to provide an improved desolderer where the rear portion of the solder transfer tube is raised to the solder melting temperature shortly after the tip reaches this temperature.
As discussed above, not only does a large heater tend to be inefficient, but it also tends to increase the tip-to-grip dimension. That is, this dimension tends to be increased in order to provide a sufficiently long path (that is, sufficiently drop the temperature) from the heater to grip 32 whereby the grip may be maintained at a comfortable temperature for the operator. In the FIG. 1 desolderer, circumferential slits 64 are employed to assist in dropping the temperature along the support path which extends from heater 52 to handle 32 via sleeve 62, plate 18, screws 22, plate 20 and hub 28. Further, the air space between plates 18 and 20 is also an important factor in dropping the temperature along the foregoing path. Nevertheless, in the FIG. 1 embodiment, sleeve 62 has been elongated and preferably provided with circumferential slits 64 to assist in lowering the handle temperature to a comfortable level. However, this does result in a lengthening of the tip-to-grip dimension with an attendant diminution in operator control over the desolderer. Thus, by being able to employ a smaller heater in accordance with an important aspect of this invention, sleeve 62 need not be so long nor need it be provided with elongated slits 64 and yet the temperature at handle 32 can be reduced to a point comfortable for the operator.
Another factor which tends to raise the temperature of the handle 32 is the presence of the heated rear end portion 51 of tube 50 within the handle as can be seen in FIG. 1. As stated above, the rear portion 51 must be maintained at a solder melting temperature (typically 375.degree. F.) while the grip should be at a temperature of no more than 120.degree. F.
Accordingly, it is another important object of the present invention to provide an improved desolderer where in conjunction with other features of the invention, the rear end of tube 50 is not disposed within handle 32 and where it may, for example, be disposed within air space 16 or within sleeve 62 to thereby remove it from the handle and thus prevent it from tending to raise the handle temperature to a level uncomfortable for the operator.
There has now been described two paths by which heater 52 can heat handle 17 to an uncomfortable level. The first one is via the support path including sleeve 62, plate 18, screws 22 and hub 28, while the second one is via tube 50 to rear end portion 51.
It is a further important object of this invention to provide an improved desolderer whereby either or both of these paths are modified to thereby prevent the tendency for the handle temperature to rise to an uncomfortable level and/or to substantially lessen the tip-to-grip dimension of the improved desolderer compared with conventional desolderers.
As stated above, it is necessary to maintain the inner walls from tip 12 to rear end 51 of tube 50 at the solder melting temperature. Otherwise, the molten solder tends to re-solidify and clog tube 50. However, the necessity of maintaining rear end 51 at the solder melting temperature introduces a complication in that the seal surface A (FIG. 1) between seal 30 and rear end portion 51 is also raised to approximately this high temperature. Hence, there is a tendency for seal 30 to be short-lived since it is separated from the interior wall of tube 50 only by the thickness of the tube. From the foregoing it can be appreciated there are conflicting requirements to be met at the rear portion of tube 50. First, portion 51 should be hot enough to ensure that the solder is still in its molten state as it is ejected into collector tube 72. However, portion 51 should be cool enough to permit the formation of an effective, long-lived seal at the front end of collector tube 72. Otherwise, the vacuum applied through fitting 19 will not be efficiently transmitted to tip 12. Although there are provisions in U.S. Pat. No. 3,163,145 and U.S. Pat. No. 3,970,234 (assigned to the assignee of the present invention) for providing a separate seal point on the transfer tube, there is no explicit recognition in either of these patents of substantially dropping the temperature at the seal point with respect to the transfer tube to thereby provide a relatively cool seal point.
Accordingly, it is another important object of the present invention to provide an improved desolderer wherein the solder can be maintained in a molten state until it reaches the collection tube while at the same time the forward end of the tube can be sealed at a point which is maintained at a temperature which enhances seal longevity and effectiveness.
As discussed above, there are basically two rearward heat paths from heater 52 of FIG. 1. One extends to handle 17 via the support path (that is, sleeve 62, screws 22 and hub 28) while the other extends to solder collector tube 72 via tube 50 and seal 30. As also discussed above, the latter path serves two purposes which tend to conflict with one another--that is, (1) the maintenance of the solder in a molten state until it reaches tube 72 and (2) the provision of a surface upon which seal 30 can be mounted.
Hence, in accordance with a further important object of this invention there is provided an improved desolderer wherein three separate paths are provided. The first of these paths generally corresponds to the support path defined by sleeve 62, plate 18, screws 22, plate 20 and hub 28 of FIG. 1. The second of these paths is employed solely for the purpose of maintaining the solder in a molten state until it reaches solder collector tube 72 and the third path is employed for providing a surface upon which the forward end of collector tube 72 can be sealed.
It is a further object of this invention to provide an improved desolderer wherein the path including sleeve 62 of FIG. 1 also includes means for providing a seal for the forward end of collector tube 72 whereby only two paths extend rearwardly from heater 52.
From the foregoing, it can be seen that in addition to the paths extending rearwardly from the heater, there is, of course, the forward path extending to the tip. Accordingly, it is a further important object of this invention to so implement the various paths extending from the heater that the most heat is directed to the tip whereby the highest temperature of the desolderer is located at the tip. The path which draws the next greatest amount of heat extends through the transfer tube whereby the solder may be maintained in a molten state until it is ejected from the tube into the solder collector tube. The path which draws the least amount of heat is that which is connected to the seal for the forward end of the solder collector tube. If the support path including sleeve 64 is not also the path to the seal, the support also draws a small amount of heat.
Together with the above characteristics, it is an important object of this invention to provide a desolderer having all or most of the following features: (1) short tip-to-grip dimension, (2) small heater, (3) comfortable handle temperature, (4) solder maintained in molten state until ejected into solder collector tube, (5) rear end of solder transfer tube reaches solder melting temperature shortly after tip does whereby operator may, for example, use desolderer as soon as solder is quickly melted, (6) seal at forward end of solder collector tube is maintained at a relatively cool temperature and (7) tip is maintained at a higher temperature than rear end of solder transfer tube, which in turn is maintained at higher temperature than seal point for forward end of solder collector tube.
It is a further object of this invention to provide an improved desolderer combining all or many of the above features wherein the desolderer may be of (1) the in-line type (either straight or curved) disclosed in aforementioned U.S. Pat. No. 3,392,897, where the solder collector is disposed within the handle, (2) the parallel collector tube type as disclosed in aforementioned U.S. Pat. No. 3,163,145 (which is incorporated herein by reference) where the collector tube is outside and usually parallel to the handle although it need not necessarily be parallel or (3) a "hammer head" type where the heating element is arranged at an angle with respect to the handle and where the collector tube is typically parallel to the handle, the "hammer head" type (3) differing from the parallel collector tube type (2) basically in that in the type (2) desolderer the heating element is substantially aligned with the handle while in the "hammer head" type (3), the heating element is angularly disposed with respect to the handle.
It is a further object of this invention to provide an improved heater assembly for use in a desolderer, the heater assembly including at least a heating element and a solder transfer means where the forward end of the solder transfer means is adapted to receive a desoldering tip and where the thermal characteristics of the rear end portion of the solder transfer means are such that the heating element raises the rear end portion of the solder transfer means to a solder melting temperature shortly after the tip reaches this temperature.
It is a further object of this invention to provide an improved heater assembly which is adapted to receive a seal mounting means which provides a sealing surface for a seal for the forward end of the solder collection chamber of a desolderer, the sealing surface being separated from the path through which molten solder traverses in the desolderer.
Other objects and advantages of this invention will be apparent from a reading of the following specification and claims taken with the drawing.